John B. Connally put his Texas stamp of approval on Ronald Reagan today, saying that the former California governor had the broadest appeal of any Republican presidential candidate among Democrats and independents.

Connally endorsed Reagan at a joint news conference here, then campaigned with him at a $200-a-person airport reception and a $1,000-a-couple reception in Longview.

"You better than anyone else have a chance to win the election this fall . . . and I want to be a part of it," Connally said. "I think this country desperately needs a change."

The Connally endorsement was frosting on the cake for the Reagan organization in Texas, where Reagan swept 100 delegates against then-president Ford in 1976 and where he is favored at the May 3, primary to win the state's 80 GOP delegates this time.

George Bush has been slow to get his campaign going in the state he represented for two terms as a congressman, and John B. Anderson is not on the ballot. But Connally remains a respected political force here despite his dismal showing in the primaries, and his endorsement was coveted and welcomed by the Reagan forces.

"It's a nice thing overall, both for the primary and the general" said Reagan state chairman Ernie Angelo. "It makes Reagan's candidacy that much stronger."

Connally said that he had taken the initiative in endorsing Reagan, had not asked for anything in return and didn't expect either to be the vice presidential nominee or a member of the Reagan cabinet, if there is one. Reagan said he hadn't ruled out anyone for vice president but declared that Anderson had ruled out him and other Republicans for the fall campaign.

Connally dropped out of the GOP race after spending $11 million and winning a single delegate in Arkansas. He abandoned his candidacy after Reagan beat him in the March 8, South Carolina primary, an open primary that Connally said demonstrated Reagan's appeal to Democrats and independents.

"You have built a base of support among average Americans, what I call middle America, which is unprecedented in modern times and certainly unprecedented in the Republican Party," Connally said to Reagan. ". . . . It's obvious to me that you are indeed speaking for a broad, segment of Americans today who want a change."

Connally was smiling and in apparent good humor throughout the day as he campaigned alongside the man who had driven him out of the GOP presidential race. But Connally's characteristic belief in his own abilities came to the fore when a reporter asked him if he thought Reagan was the most capable man to lead the country.

"I think he's the second best man I can think of," Connally said with a broad grin to the laughter from reporters and Reagan.